Nanoporous carbon membranes are known in the art. These membranes comprise films of carbon, or carbon based materials, having a pore structure in the nanoscale range. As is understood herein, a nanoscale range generally refers to features on the submicron scale. As is known in the art, nanoporous, carbon based membranes are fabricated by pyrolyzing appropriate organic materials, typically polymers, in a non-oxidizing atmosphere. The resultant membranes are comprised entirely, or primarily, of carbon and manifest an active surface and a controlled pore structure. Typically, such membranes are prepared upon a support member such as a body of stainless steel. Membranes of this type are disclosed, for example, in U.S. Pat. Nos. 5,104,425; 5,354,547 and 5,431,864.
Nanoporous carbon membranes have been found to have utility as molecular sieves. Owing to their controlled pore size, these membranes effectively allow for the separation or enrichment of composite gas mixtures. Nanoporous membranes are also employed in chemical reactors and in catalytic systems.
One problem that has plagued prior art nanoporous carbon membranes is the fact that their coefficient of thermal expansion frequently differs from that of a substrate upon which they are disposed. Furthermore, the carbon itself tends to be relatively brittle; hence, thermal cycling can cause cracking of these membranes. Also, in some instances, gas permeability of these membranes is undesirably low thereby limiting their utility.
As will be explained in detail hereinbelow, the present invention provides for improved nanoporous carbon membranes, and specific methods for their manufacture. The membranes of the present invention incorporate nanoscale particulate matter therein, and the presence of this material tends to relieve stresses in the membrane and hence reduces cracking during thermal cycling. Furthermore, the presence of the particulate material enhances the gas permeability of these membranes. In some instances, the particulate material may be chosen so as to actively enhance the chemical, physical or catalytic effects of the membrane material. These and other advantages will be apparent from the discussion hereinbelow.